Influential French naturalist and evolutionary theorist.
Initially a self-taught botanist working under the patronage of Buffon, he took up invertebrate zoology upon appointment to the Muséum d'histoire naturelle.
Lamarck was a prodigious taxonomist and wrote lengthy, poorly received theoretical discourses on mineralogy and meterology, but is best known for his sweeping evolutionary theory, which he developed shortly after 1800.
Although not the only transmutationist of his time - most of his colleagues a the Muséum d'histoire naturelle accepted at least a limited form of the idea - Lamarck was the first to seriously suggest that man and all other species may have evolved instead of being specially created.
His theory of evolution, developed after the turn of the century, was very different from that of later "Lamarckians" and did not particularly emphasize the inheritance of acquired characters, which was already widely accepted at the time.
Lamarck called for spontaneous generation of numerous lineages that evolved under the influence of vital fluids up one or a few scales of complexity. Thus, living forms did not share a single physical ancestor, but did form evolutionary gradients.
Lamarck's main opponent was G. Cuvier, who initially responded with public silence and private condemnations.
Three years after Lamarck's death Cuvier denounced the theory in a nominal "elogy" to his departed colleague.
Lamarck's arrogance, wordiness, political isolation, and reputation for wild theorizing left him with few allies before his death, but later in the century he was perceived as perhaps even more important than Darwin as a founder of evolutionary biology.